Dr. Jaudy explains some of the many causal roots of depression.
Depression is associated with myriad conditions and is often the result of improper neural signaling. In this article, I will discuss some of the many causes of depression and how it relates to other digestive and neurological conditions.
Traditionally and conventionally, depression was (and often still is) considered as a psychological disorder. However, recent research in neuroscience is increasingly providing evidence that depression and other mood disorders are due to underlying disorders, either physiological, neurological, or both, that lead to psychological symptoms, such as depression. 1 - 5
According to the Anxiety and Depression Association of America, there are many health conditions that include depression (and anxiety) among their lists of symptoms. These include chronic fatigue syndrome 6, chronic pain disorders (including fibromyalgia, migraines, back pain, etc.) 7, irritable bowel syndrome 8, sleep disorders 9, diabetes 10, movement disorders 11, kidney diseases 12, balance disorders 13, learning disorders, addictions, plus many others.
So the question is: why do all of these conditions and others include depression among their symptoms? The answer is that there are many different causes to depression. All of the conditions listed above are due to physiological and neurological problems. Although depression is thought to be psychological conditions, meaning that it is a problem in your thought process, the list of conditions above shows that there is likely a physiological and neurological underlying problem that contributes to this seemingly psychological symptom.
The Physiology and Neurology of Depression
The hallmark of depression is alteration of brain neurochemical transmission. This neurochemical transmission takes place via neurotransmitters, such as GABA, dopamine, serotonin, norepinephrine, epinephrine, acetylcholine and histamine. 14 - 17 These neurotransmitters play a role in the development of depression disorders.
Neurotransmitters are brain chemicals and they communicate information throughout the brain and body. They are responsible for your heartbeat, your breathing, your digestion, your sleep, your ability to concentrate, your mood, and all other functions of your body.
Good health requires that all of your body’s systems and chemicals (including neurotransmitters) be in equilibrium, or homeostasis. When this homeostasis is lost, any number of symptoms may emerge, including depression. When the levels of neurotransmitters in your body are lower or higher than they should be, your body loses homeostasis and you begin to lose your health.
The Limbic System
Neurotransmitters are affected by the limbic system. The limbic system is responsible for a variety of tasks including memory, learning, social processing, and even your mood and emotions. When the processes and functions of your limbic system are altered, your neurotransmitters become altered as well.
In the previous section, we discussed the myriad of conditions that include depression among their symptoms. The reasons that depression is a symptom associated with these conditions differ depending on the individual. Everyone is different, with their own unique biochemistry, genetic predispositions, environments, behaviors, and so on. Just to give you an example of how these conditions may affect your neurotransmitters, leading to depression, consider something like vascular diseases. When your blood is unable to be properly shunted to the brain, fuel cannot be properly transmitted to brain cells, which rely on their electrical energy to secrete neurotransmitters. So, you may start with a kidney disease, diabetes, neuropathy, or any other condition that affects your vascular system, and this can lead to decreased blood flow to the brain, leading to decreased secretion of neurotransmitters, which in turn can lead to depression, among other symptoms.
Gas Exchange and Its Relationship to Depression
In addition to problems with blood flow to the brain, abnormalities in the gases present in the blood (oxygen and carbon dioxide) plays a major role in depression. Cells that produce neurotransmitters require fuel in the form of oxygen. In order for the proper levels of oxygen to be present in the blood that reaches these cells, there needs to be functional gas exchange processing. This takes place through a series of organs and centers in the brain including respiratory centers, cardiac centers, the lungs, the liver, and kidneys. If there is a problem in any of these regions, depression may develop.
Dysfunctions in gas exchange and/or changes in breathing activities can lead to higher or lower oxygen levels or higher or lower carbon dioxide levels in the blood. This may lead to anxiety or depression because the cells aren’t receiving the proper fuel they need to secrete the proper neurotransmitters. Alterations in respiration may also lead to anxiety simply because you are unable to breath. This is commonly experienced while sleeping, because as the autonomic nervous system takes over, all your functions slow down, including breathing. If you are not receiving the proper levels of oxygen and you sleep, it may lead to even more depletion of oxygen. This can lead to anxiety or panic attacks at night. Furthermore, once you begin to experience anxiety, you begin to feel more anxious because of your anxiety, so it’s perpetual .
When you have problems with gas exchange, this increases your breathing rate causing hyperventilation. As a result, the amount of blood that reaches the brain decreases causing depression and other mood-related symptoms. When you have problems in your life, whatever they may be, this leads to stress which activates your limbic system, which in turn affects the heart causing your heart rate to increase. This affects the blood cycle and the amount of oxygen that reaches your brain decreases, which also can lead to depression and anxiety.
The Human Body is an Integrated Machine
So, there is no simple answer to what causes depression, but it should be clear to you that depression and other mood-related symptoms are not solely psychological. Instead, these symptoms are due to physiological, chemical, and neurological dysregulation. What’s important to understand here is that no symptom is due to a single dysfunction in a single brain or body region. The human body is an integrated, interconnected machine that depends on the functions of all of its parts. This is why many theories or hypotheses about the causes of symptoms, such as depression, are inelegant and often disproven. For example, it was once believed that depression was solely due to decreased serotonin levels, which has been disproven. A more recent hypothesis is that a decrease in the genesis (growth) of new neurons in the hippocampus is the cause of depression. 18 While decreased neurons in the hippocampus does play a role, it is not likely going to be proven as the one and only cause. We must always view the human body as it is: an integrated whole. We cannot just look at one region, we must look at all regions and how all these regions and components interact to produce function.
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- Centers for Disease Control. Chronic Fatigue Syndrome. Accessed May 26, 2014. Available at: http://www.cdc.gov/cfs/management/treating-symptoms.html
- Anxiety and Depression Association of America. Chronic Pain. Accessed May 26, 2014. Available at: http://www.adaa.org/understanding-anxiety/related-illnesses/other-related-conditions/chronic-pain
- Anxiety and Depression Association of America. Irritable Bowel Syndrome. Accessed May 26, 2014. Available at: http://www.adaa.org/understanding-anxiety/related-illnesses/irritable-bowel-syndrome-ibs
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